Methods of constructing a traveling wave tube



May 1 1964 A. COHEN ETAL 3, 3 0

METHODS OF CONSTRUCTING A TRAVELING WAVE TUBE Filed March 8, 1962 2Sheets-Sheet 1 May 12, 1964 A. COHEN ETAL METHODS OF CONSTRUCTING ATRAVELING WAVE TUBE 2 Sheets-Sheet 2 Filed March 8, 1962 x a? W \W W \i\17 A m 0 3 M U mw N Vf P N 5% 0 5.7 MW Maw MP%@ United States Patent3,132,410 METHODS OF CONSTRUCTING A TRAVELING WAVE TUBE Aaron Cohen, SanDiego, Calif., Maurice F. Liscio, West Orange, N.J., and Paul Okstein,Brooklyn, N.Y., assignors, by mesne assignments, to the United States ofAmerica as represented by the Secretary of the Navy Filed Mar. 8, 1962,Ser. No. 178,515 3 Claims. (Cl. 29-2514) The present invention relatesto traveling wave tubes and more particularly to methods of constructinga helix assembly in traveling wave tubes.

A traveling wave tube is a device which provides for the continuousinteraction between an electron beam and an electromagnetic wave so thatthe wave is amplified. In order that such interaction be obtained, theelectromagnetic wave must be retarded or slowed so that its phasevelocity will be approximately the same as the speed of the electrons inthe beam. The most common type of retarding structure used in travelingwave tubes is a metal helix whose diameter and pitch are set to producethe desired axial phase velocity of an electromagnetic wave propagatedtherealong. Since the structure of the helix is an elongated one, caremust be observed in the fabrication thereof to assure that the desiredpitch and diameter will be maintained throughout its entire length so asto accordingly provide the proper phase relationship between theelectromagnetic wave and the electron beam.

One heretofore known method of supporting a helix assembly consists inusing three of four ceramic rods which are attached externally to thehelix turns. The rods are rigidly attached lengthwise of the helix toproduce a support which is actually integrated with the slow-wavestructure. These rods are attached to the helix with a thin glasscoating. However, this method of assembly requires that both the rodsand the helix be precision ground so as to avoid breakage due tomisalignment. Another disadvantage of using rods is that their relativelow strength limits the type of application to which a traveling wavetube may be put. A further disadvantage of using ceramic support rods isthat the diameter of the tube is materially increased.

In the present invention, the wire helix is supported by a vitreous tubehaving a plurality of longitudinal convex ribs which engage with thewire helix. In one embodiment, a plurality of longitudinal ribs areprovided in the vitreous tube prior to assembly with the wire helix, andafter assembly pressure is applied during heating, and the ribs areembedded around the wire helix. In another embodiment, the plurality ofribs are formed during the heating and pressing operation. In thepreferred embodiment of using a vitreous tube that has preformedlongitudinal ribs, the wire helix is inserted into the vitreous tubewhich is of suflicient size so that the longitudinal ribs slightly clearthe outside diameter of the wire helix. The tube assembly is then placedin an embedding fixture that has a top and bottom block. Each block isprovided with a trough that is slightly smaller in diameter than theoutside diameter of the vitreous tube and the troughs are provided witha number of longitudinal ribs equal in number to the number of ribs inthe vitreous tube. With the tube assembly in place, the longitudinalribs in the troughs contact the outer surface of the vitreous tube andthe top and bottom blocks are separated by a predetermined amount. Uponheating, the vitreous tube softens and the top block moves down underits own weight until it rests on the bottom block. The longitudinal ribsin the vitreous tube are pressed into the coils of the wire helix andthe outside diameter of the vitreous tube is nested into the troughs ofthe top and bottom blocks. The depth to Patented May 12, 1964 which thelongitudinal ribs penetrate between the turns of the wire helix isdetermined by the original gap between the top and bottom blocks and thesize of the longitudinal ribs in the troughs.

It is therefore a general object of the present invention to provide animproved method of assembling a wire helix in a traveling wave tube.

Another object of the present invention is to provide an improved methodof embedding a wire helix in a vitreous tube.

Otherobjects and advantages of the present invention will be readilyappreciated as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawing wherein:

FIGURE 1 is a partial assembly before heating;

FIGURE 2 is a sectional view of FIGURE 1;

FIGURE 3 is a partial perspective view showing a tube assembly afterheating;

FIGURE 4 is a sectional view of FIGURE 3;

FIGURE 5 is an end view showing another embodiment of the presentinvention;

FIGURE 6 is a sectional view taken on line 66 of FIGURE 5;

FIGURE 7 is an end view of another embodiment showing an assembly priorto heating; and

FIGURE 8 is an end view of the embodiment of FIG URE 7 after heating.

Referring now to FIGURES 1 through 4 of the drawing that show apreferred embodiment of the present invention, a wire helix 11 isinserted in the bore of a vitreous tube 12, such as tubular glass, thatis provided with three longitudinal convex ribs 13. A mandrel 14 may beprovided to preserve the as-wound accuracy of the wire helix 11 in thetube 12. The assembled unit of the mandrel 14, wire helix 11, and tube12 are placed in a fixture 15 comprised of a bottom portion 16 and a topportion 17, and as shown in FIGURE 1 of the drawing, a smallpredetermined gap 18 exists between the top and bottom portions of thefixture 15. Three convex ribs 19 are provided longitudinally in fixture15 and are spaced so that one each will be opposite each convex rib 13.Fixture 15 is placed in a heat environment, such as a furnace, and asthe vitreous tube 12 softens, the top portion 17 moves down under itsown weight until it rests on the bottom portion 16. As the vitreous tube12 softens, the convex ribs 19 in fixture 15 presses the longitudinalconvex ribs 13 into engagement with the wire helix 11 and the wire helix11 becomes embedded in the ribs 13, as shown in FIGURE 4 of the drawing.

Referring now to FIGURES 5 and 6 of the drawing, another embodiment isshown for assembling a wire helix in a vitreous tube. Fixture 21, whichis comprised of an upper half 22 and a lower half 23, can be separatedto allow the placement of a wave tube assembly in a cylindrical opening24. An oversized recess 25 is provided on one end to permit the gun bulb26 to clear the fixture. A plurality of slots 27 are provided in fixture21 and extend from the outer periphery to the cylindrical opening 24. Anembedding blade 28 is provided in each slot, and each blade is providedwith a head portion 29 that cannot enter the slot 27.. Thus it can beseen that the embedding blades can travel only a limited distance.

In operation, a wire helix 11 is slip-fitted inside a vitreous tube 31and placed in the cylindrical opening 24. The embedding blades 28 arethen inserted in slots 27 with the ends thereof being in contact withthe vitreous tube 31. The fixture is then placed in a base 32 thatengages with the head portions 29 of two of the embedding blades 28. Aweight 33 is placed on top of the third embedding blade 28. The fixtureis then placed in a heat perspective view showing a tube environment,such as an oven, and as the vitreous tube 31 softens, the embeddingblades 28 force the softened vitreous tube against the wire helix andupon cooling the wire helix is embedded in the vitreous tube 31.

Another embodiment of the present invention is shown in FIGURES 7 and 8of the drawing. A wire helix 11 is supported inside a precision glasstube 41 by a plurality of longitudinal metal strips 42. The strips arespaced so as to provide gaps 43 through which the glass can move toembed the Wire helix 11. A mandrel 44 may be provided to preserve theas-wound accuracy of the helix. The processing can be accomplished ineither the fixture shown in FIGURE 1 of the drawing or the fixture shownin FIGURES 5 and 6 of the drawingv FIGURE 8 of the drawing shows thecomplete tube assembly after the heating and cooling steps and after themandrel 44 and strips 42 have been removed by selective etching. By wayof example, the wire helix 11 might be made of tungsten and the strips42 and mandrel 44 might be made of molybdenum.

It can thus be seen that the present invention provides an improvedmethod of embedding a wire helix in a vitreous tube and that theassembled unit is small and compact. Obviously many modifications andvariations of the present invention are possible in the light of theabove teachings. It is therefore to be understood, that within the scopeof the appended claims, the invention may be practiced otherwise than asspecifically described.

What is claimed is:

1. A method of constructing a helix assembly comprising:

(a) placing a wire helix in a vitreous tube having a plurality oflongitudinal convex ribs integral with the inner periphery thereofwhereby said wire helix is supported by said convex ribs,

(b) heating said vitreous tube to a viscid condition,

and

(c) then applying pressure to the outer periphery of said vitreous tubeat a line where each convex rib is positioned while said tube is in aviscid condition whereby said longitudinal convex ribs are embedded withsaid wire helix.

2. A method of constructing a helix assembly as set forth in claim 1wherein said helix is supported by a mandrel during the heating of saidvitreous tube.

3. A method of constructing a helix assembly comprising:

(a) placing a wire helix in a vitreous tube having a plurality oflongitudinal convex ribs integral with the inner periphery thereofwhereby said wire helix is supported by said convex ribs,

(11) then positioning said vitreous tube in a cylindrical fixture havinga plurality of embedding blades the ends of which contact the outerperiphery of said vitreous tube at lines where said convex ribs arepositioned, and

(c) then heating said vitreous tube while in said fixture whereby saidembedding blades move a predetermined distance thereby embedding saidconvex ribs into said Wire helix.

References Cited in the file of this patent UNITED STATES PATENTS2,706,366 Best Apr. 19, 1955 2,752,731 Altosarr July 3, 1956 2,767,344Hines Oct. 16, 1956 2,806,170 Bianculli Sept. 10, 1957 2,845,690Harrison Aug. 5, 1958 2,869,217 Saunders Jan. 20, 1959 2,879,436 GeislerMar. 24, 1959 2,943,228 Kleinnan June 28, 1960

1. A METHOD OF CONSTRUCTING A HELIX ASSEMBLY COMPRISING: (A) PLACING AWIRE HELIX IN A VITREOUS TUBE HAVING A PLURALITY OF LONGITUDINAL CONVEXRIBS INTEGRAL WITH THE INNER PERIPHERY THEREOF WHEREBY SAID WIRE HELIXIS SUPPORTED BY SAID CONVEX RIBS, (B) HEATING SAID VITREOUS TUBE TO AVISCID CONDITION, AND (C) THEN APPLYING PRESSURE TO THE OUTER PERIPHERYOF SAID VITREOUS TUBE AT A LINE WHERE EACH CONVEX RIB IS POSITIONEDWHILE SAID TUBE IS IN A VISCID CONDITION WHEREBY SAID LONGITUDINALCONVEX RIBS ARE EMBEDDED WITH SAID WIRE HELIX.